During Phase I, we developed and built a compact, portable, Frequency- Domain Tissue Spectrometer. The instrument provides, in real time, the absolute values of the scattering and absorption coefficients of oxy- and deoxy-hemoglobin in tissues and, hence, the hemoglobin saturation and the total hemoglobin content. Selected researchers used the instrument for the study of tissue oxygenation in muscles of normal and dystrophic subjects, brain region, for the mapping of the optical parameters of breast and the study of peripheral vascular disease (PVD). Of the many potential applications of the new instrument, we choose the early detection of PVD for the Phase II continuation of this project. This choice is dictated by the importance of the problem and by the successful use of the instrument for PVD early detection during clinical tests. During the Phase II, IFS intends to expand the instrument capabilities, perform exhaustive laboratory tests, and build a clinical instrument for the study and the early detection of PVD. Practical feedback for the instrument development will be provided by climb studies conducted at the University of Texas, Dallas; research aspects related to the interaction of light with tissues will be studied at the University of Illinois at Urbana-Champaign. PROPOSED COMMERCIAL APPLICATION: Non-invasive, absolute measurement of oxygenation state of tissues and determination of blood volume. Determination of tissue absorption and scattering coefficients for accurate setting of laser power in surgery and photodynamic therapy. Assessment of drug delivery to target tissues.